Implanted Magnets for Prosthetic Control

Engineers at MIT have developed a system that could let users of robotic prostheses to more sensitively control their bionic limbs. The technology involves implanting pairs of small magnetic beads into muscles. When the muscles contract, the beads move closer together, allowing prosthetic devices to more precisely calculate a user’s intentions and mirror these.

Current systems measure the electrical activity in muscles, but this is not as accurate as measuring actual muscle movement. Medgadget last covered the technology in August 2021, and since then, the researchers have tested it in turkeys, showing that the implanted magnets do not cause inflammation or irritation. Importantly, they can assist in very accurately measuring muscle length as the turkeys traversed an obstacle course (yes, really), reflecting real-world conditions outside the lab.

Each year seems to bring new improvements in assistive tech, such as novel robotic prostheses and wheelchairs. Hopefully, in the future, patients who lose a limb, or experience muscle weakness or paralysis, will have a full suite of advanced robotic prostheses at their disposal, bringing immediate and significant convenience and independence. Until then, we can plot how such technologies advance.

This latest development seeks to improve on the way that robotic prostheses can sense their user’s intentions and move accordingly. At present, such devices typically sense the electrical activity of the muscles using a process called known as surface electromyography. However, this approach does not account for muscle activity, in terms of velocity of movement and muscle length during contraction.

To address this limitation, the MIT researchers hit on a new approach that they call magnetomicrometry. This involves simple pairs of implanted magnetic beads that move together as a muscle contracts and further away from each other as it relaxes. The idea is to empower robotic prostheses to detect the magnetic signal from the muscle and infer the user’s intentions.

While this may sound great in practice, and the researchers have shown that it works under controlled conditions in the lab, it is important to test technologies in a real-world context. So, in this spirit, these researchers implanted the magnetic beads into turkeys, and set them to work running around an obstacle course. The birds ran and jumped over obstacles, while the researchers assessed if the magnetic beads could provide accurate readings on muscle length.

Happily, the system was very useful in assessing muscle length, and could provide a measurement in less than a millisecond. Moreover, it compared favorably with more traditional equipment in terms of accuracy. The researchers also investigated the effects of the beads on the body, and found that they do not cause irritation in the muscle, suggesting that they are suitable for long-term implantation.

Here’s an MIT video about the technology: